There are a great variety of wireless communication systems being used in the world today, such as Global System for Mobile Communication (GSM), Digital Advanced Mobile Phone Service (DAMPS), Personal Handy System (PHS), Personal Communication Services (PCS), Land Mobile Radio (LMR), Special Mobile Radio (SMR) and two way paging to name a few. The consumer would like their phone or pager to reliably work anywhere in the world for a long time. One of the keys to the amount of time that a phone can go without being recharged is the amount of current the oscillator draws when the phone is in receive mode.
Typically, the Voltage Controlled Oscillator (VCO) generates the Local Oscillator (LO) signal for transmit and receive functions in mobile radio RF circuitry. The VCO is typically left on in the standby mode when the phone is neither transmitting or receiving.
The prior known methods to conserve current in VCO designs or implementation in a phone have consisted of putting a phase shift network in the feedback circuitry or switching the transmit VCO off along with the power transmitter to conserve dc power. U.S. Pat. No. 4,621,241 to Kiser discloses a VCO with a phase shift network in the feedback circuitry.
The disadvantage of using a phase shift network in the feedback network is the current consumption is fixed and the oscillator current and performance must be optimized to meet the performance requirements when operating in the normal power consumption mode.
The oscillator is typically used in a phase locked loop (PLL). The disadvantage of turning the transmitter oscillator off with the power transmitter is that the PLL takes time to lock after the oscillator is turned back on, meaning lost transmit time and channel inefficiency.
A known power level is needed in the oscillator to meet the phase noise requirements for good fidelity and high data rates when the phone is transmitting and receiving. This is the normal power consumption mode. Oscillation will be sustained in the oscillator and the PLL will remain locked at a lower power level when the phone is not transmitting or receiving. The phase noise is, however, degraded in this lower power consumption mode. An oscillator is needed with switching means to switch between the normal and lower power consumption modes in order to conserve power without loss of transmit time or loss of channel efficiency.